Electrosurgical procedures performed with an electrosurgical generator and an electrosurgical pencil or handpiece require that the surgeon have control over the application of power directed to the human or animal patient. Specifically, the electrosurgical energy output of the electrosurgical generator can be set at the generator control panel which is remote from the sterile field of the operating site. It is also necessary that the application of the electrosurgical energy delivered to the handpiece be controlled, i.e. started and stopped as desired in the sterile field by the surgeon during the surgical procedure. Wherefore the surgeon has full control over the positioning of the handpiece and more particularly an electrosurgical electrode thereof and the initiation and completion of energy delivery.
Electrosurgical handpieces are common surgical instruments that need to be made in high volumes at relatively low costs. In addition the function of the handpiece must be reliable and safe. With regard to the former the delivery of electrosurgical energy as required should be consistent notwithstanding the demands of switching at high frequency, 500 kilocycles, and at high power up to three hundred watts. The switch mechanism is not only ergonomically oriented on the handpiece but also requires an indicative feel of on and off, a tactile manifestation of travel distance. The control must also be reliable and properly functional to indicate to the surgeon with the certainty that the control is operating as needed. In addition the switch has to prevent any misdirection or inadvertent application of electrosurgical energy to be safe.
Electrosurgery is the application of a radio frequency electrical energy to a surgical site on a human or animal patient for tissue cutting, coagulation, or a blend thereof. In monopolar mode the radio frequency energy that is generated by the electrosurgical generator is applied to tissue from an active electrode held in the handpiece by the surgeon, and is collected from a dispersive electrode attached to the patient. A small contact area of the active electrode causes a high current density so that a spark enters the tissue at the surgical site. This spark causes intense localized heating, eschar, fulguration and other effects, to achieve the cutting and/or coagulation. The dispersive electrode collects the energy returning it to the electrosurgical generator to complete an electrical circuit. The dispersive electrode is of a significant size so that the energy density collected thereby is low enough to avoid any surgical or heating effect that would burn.
A burn will develop if the power delivered to the tissue and after its passage through the body results in a high energy density at the exit so that localized tissue heating occurs. This situation happens when the energy is allowed to pass at a location other than the dispersive electrode such a condition is called leakage. A burn from leakage can be quite severe as the patient is anesthetized and will not react thereto. The burn area is frequently covered so the doctor or surgical attendants will not see it until it is too late to take corrective action.
Another potential path for leakage burns is to the surgeon through contact with the active electrode, the switch contacts, the conductors which supply the radio frequency, high voltage electrosurgical energy to the handpiece. Leakage in that circumstance may harm or burn the surgeon or one of the surgical attendants in contact with the switch contacts, the active electrode or its supply conductors and a ground. It is for this reason that leakage or alternate path energy flow in electrosurgery are of considerable concern and efforts are made to monitor and control leakage.
The early electrosurgical generators were of a ground referenced design. Being ground referenced, the return for the electrosurgical generator and the dispersive electrode were both connected to earth or ground. The ground referenced arrangement was satisfactory provided that no other point on the patient was grounded. When a monitoring electrode, i.e. EKG, was used during the electrosurgical procedure, and the monitoring electrode was referenced to ground, some portion of the electrosurgical energy could flow to ground through the monitoring electrode, instead of the preferred path back through the dispersive electrode. Since monitoring electrodes usually have small contact area, the current density at their contact may be sufficient to develop enough energy density to result in a burn. An even worse condition occurs if the electrosurgical generator connection to the dispersive electrode is accidentally separated. Thus, with no direct energy path back to the electrosurgical generator, all of the power travels through any alternate grounded paths, such as through the monitoring electrodes, the surgeon and/or the surgical table or perhaps through the handpiece switch. Severe burns are a possible result.
In an effort to reduce the risks associated with the ground referenced electrosurgical generators, the power output circuit of the electrosurgical generator was isolated from any other ground. Output isolated electrosurgical generators were a significant step in reducing the risks associated with alternate path burns, because the electrosurgical energy exiting the patient was more likely to flow through the dispersive electrode to complete the circuit and not through any other ground referenced points when returning to the electrosurgical generator. If the generator connection to the dispersive electrode became disconnected, a significant portion of the electrosurgical energy flow from the electrosurgical generator would stop.
Although isolated output electrosurgical generators was an improvement over the previous ground referenced units, a problem remained because the isolation from ground was not always perfect. At the relatively high frequencies of electrosurgical current, e.g., 500 kilohertz to 1 megahertz, stray capacitance to ground allows another ground referenced path. Furthermore, the amount of stray capacitance required to create this other significant path for ground referenced energy flow is not great. Although alternate paths of energy flow are less than those flowing if the electrosurgical generator was ground referenced, a potential exists for significant patient and alternate path burns. Consequently, adequate spacing of the switch contacts and insulation thereof is essential to safe operation.
Therefore the switch in the handpiece is frequently isolated so that switching the full energy delivered by the electrode is not across the contacts thereof. Various techniques including optocoupling, low power slave circuits and the like are used. Valleylab of Boulder, Colo., the assignee, of the present disclosure has manufactured and sold many handpieces of various styles and types and has several United States patents and applications including, 3,801,766; 4,827,927; 5,015,227; Des 287,879. Against this background and with an appreciation of the problem of accurately and automatically manufacturing a switch, further significant improvements and advancements in the control of electrosurgical energy, particularly during initiation and termination of electrosurgery, are required. Described herein are a method its tool and a product produced thereby not found in the literature or practiced in the field. The literature is of interest for its teachings of the knowledge of skilled artisans at the time of this invention.